Unusual material can be magnetically and electrically polarised

A team of physicists has published a paper detailing how an iron compound can be both magnetically and electrically polarised -- an extremely rare
property that material scientists are only just starting to
understand.

The TbFeO3 compound, which is multiferroic (a material that
presents more than one ferroic parameter -- in this case magnetic
and electric polarisation), presented with very unusual magnetic
domains. Usually a material's magnetised atoms point in the same
direction until they are significantly cooled. At this point the
magnetic area is divided into sub-sections called magnetic domains
-- the atoms within each domain point in the same direction,
however different domains have atoms pointing in different
directions.

When TbFeO3 was cooled to -271C and the physicists studied it
using neutron diffraction, the magnetic domains presented "straight
as an arrow with the same distance between them", instead of the
usual "helter-skelter" format. The "walls" between these domains
were also shown to repel one another.

"We were completely stunned when we saw it," said Kim Lefmann,
physicist at the University of Copenhagen and an author on the
paper, published in the June 2012 issue of Nature Materials.

These multiferroics were first discovered in the 60s, but
researchers did not have the technology to examine them in
detail. These latest studies were carried out at the neutron
research facility Helmholtz-Zentrum in Berlin, where physicists can
study a material's atomic structure in detail using the research
reactor BER II, which generates neutrons that can be beamed towards
materials to examine them in detail, a little like a
high-resolution x-ray machine.

They found that, despite its unusual magnetic domains, TbFeO3's
atoms were ordered in the usual way, in a lattice pattern made up
of rows of the metal terbium, separated by iron and oxygen
atoms.

"The terbium walls interact by exchanging waves of spin
(magnetism), which is transferred through the magnetic iron
lattice," explains Heloisa Bordallo, a physicist at the Niels Bohr Institute
involved in the study. "The material exhibits, in a sense, the same
interacting forces that hold the particles together in atomic
nuclei".

The waves of spin -- which were shown to have an unusual order
and change directions suddenly -- cause the increase in electric
polarisation, while the interactions between the ions of the
terbium, iron and oxygen create a stronger magneto-electrical
effect than in most other materials.

Now that the physicists understand why the compound exhibits
these unusual characteristics, they plan to push their studies
forward and discover what uses it could have, for instance, in
sensor technology.